1. Field of the Invention
The present invention relates to ultrasonic vibration welders.
2. Description of the Related Art
Various ultrasonic vibration welders for welding stacked ultrasonic-weldable parts, such as metal parts or plastic parts, by applying ultrasonic vibration and welding pressure are in practical use. Japanese Patent No. 2756433 discloses one of such ultrasonic vibration welders. FIG. 10 shows a relevant part of the ultrasonic vibration welder.
Referring to FIG. 10, an ultrasonic vibration welder 100 includes a generator 101 that generates an electrical frequency, an oscillator 102 that converts the electrical frequency generated by the generator 101 into mechanical vibration, a horn 103 that amplifies the vibration, the horn 103 being fixed to the oscillator 102 at one end and thinned at the other end, a vibration transmission rod 104 joined to the thinned end of the horn 103 in such a manner that it extends perpendicularly to the axis of the horn 103, a mass 104A serving as a resonator for applying pressure, and a pressure applicator 105 connected to the mass 104A. The horn 103 and the vibration transmission rod 104 are joined together by welding or brazing. The ultrasonic vibration welder 100 further includes a chip 106 attached to an end of the vibration transmission rod 104, an anvil 107 arranged at a position facing the chip 106, and an anvil base 108 that supports the anvil 107. Parts to be welded together are denoted by W and W.
In the ultrasonic vibration welder 100, the horn 103 causes the vibration transmission rod 104 to perform flexural vibration, while the pressure applicator 105 applies welding pressure to the vibration transmission rod 104, thereby causing friction between the parts W and W. The friction generates frictional heat, which diffuses or melt-bonds the parts W and W at portions subjected to friction. Thus, the parts W and W are welded together.
The vibration transmission rod 104 of the ultrasonic vibration welder 100 has a circular cross section. This means that the vibration transmission rod 104 resonates at a single frequency when flexural vibration is applied to the central axis thereof in any direction. There is no guarantee that the vibration transmission rod 104 always vibrates in the axial direction of the horn 103, which is an ideal vibration direction, during welding. Depending on the state of the load applied to a connecting portion between the vibration transmission rod 104 and the horn 103, the vibration transmission rod 104 can vibrate in a direction oblique to the axis of the horn 103, which is not an ideal vibration direction. However, the ultrasonic vibration welder 100 has no structure for solving this problem. Accordingly, there is a problem in that the connecting portion between the vibration transmission rod 104 and the horn 103 connected to the oscillator 102 has a tendency to get damaged.
Ultrasonic vibration generated by the oscillator 102 and the horn 103 is transmitted to the chip 106 through the vibration transmission rod 104. At the same time, welding pressure is applied to the parts W and W through the pressure applicator 105, the vibration transmission rod 104, and the chip 106. This structure has the problems described below.
The chip 106, which is brought into contact with the parts W and W during welding, is attached to an end of the vibration transmission rod 104. The problems lie in the structure in which the separately formed chip 106 and vibration transmission rod 104 are connected together. Examples of methods for attaching the chip 106 to an end of the vibration transmission rod 104 include a screw-in method as shown in FIG. 10 and a taper shank method (not shown).
In the case of an ultrasonic vibration welder that employs a screw-in method, a copper washer (not shown) is disposed between surfaces to be joined by a screw. However, the copper washer is degraded by heat and ultrasonic vibration transmission stress, and therefore the ultrasonic vibration welder cannot endure long-term use (after it is used about 5000 to 10000 times). In addition, if chips are screwed into ends of vibration transmission rods with a predetermined fastening force, the orientation of chip patterns with respect to the vibration direction varies. Accordingly, an ultrasonic vibration welder that employs a screw-in method cannot be used to weld parts that require the chip pattern and the ultrasonic vibration direction to be properly set.
In the case of an ultrasonic vibration welder that employs a taper shank method, it is possible to make chip patterns be oriented in the same direction with respect to the vibration direction. However, because chips are press-fitted to vibration transmission rods, the chips tend to drop or the fitting therebetween tends to become loose if the welding pressure during vibration is low. Thus, when tuning vibration, parts to be welded need to be disposed between the chip and the anvil while sufficient welding pressure with which normal vibration can be obtained is applied thereto. Further, in the case of welding products that require application of ultrasonic vibration under low pressure, such as small parts or thin parts, it is impossible to apply normal ultrasonic vibration because the welding pressure cannot be reduced during welding. Accordingly, it is impossible to weld such products. In addition, the vibration transmission rod is not durable. Because both the ultrasonic vibration and the welding pressure are transmitted to the chip through the vibration transmission rod, when welding is performed under high pressure, a shank portion of the vibration transmission rod is deformed and expanded.
In the known ultrasonic vibration welder 100, the mass 104A is formed integrally with the vibration transmission rod 104 at the end opposite the end to which the chip 106 is attached. Thus, when the vibration transmission rod 104 needs to be replaced for the reasons described above, the mass 104A also needs to be replaced. This is not cost effective.